1. Field of the Invention
The present invention relates generally to methods and apparatus in the field of probe cards and contact cards for testing semiconductor substrates. More specifically, the present invention relates to methods and apparatus in the field of probe and contact cards that compensate for variation in the height of contacts on the semiconductor substrate under test.
2. State of the Art
For burn-in testing of semiconductor substrates, an electrical connection must be established from the contacts on the substrate to the testing device. Often a section of printed circuit board (PCB) with contacts corresponding to the substrate under test is connected to the testing device and used to make contact with the substrate. Typically the PCB is made of low cost PCB material, which creates difficulties in making it planar and also has different thermal expansion properties than the substrate under test. Typically, probe cards, or contact cards have been used to make contact from the PCB to the substrate under test to compensate for such problems.
Variation in height of the contacts of the semiconductor substrate under test, such as where the semiconductor substrate includes mounting or interconnect structures, including under bump metallization, redistribution lines, solder balls, or other connections, can result in probe cards having difficulty making and maintaining good contact. For example, as described in U.S. Pat. No. 6,535,012, in a reusable test fixture for burn-in testing, the variation in the height of contacts of a semiconductor substrate is compensated by a portion of the reusable test fixture that uses contact tips or flexible contact tips for contacting the contacts on semiconductor devices and contacts on a wafer. If desired, an elastomeric mat having conductive patterns thereon corresponding to conductive pads or contact areas on the wafer may be used with flexible contact tips on a portion of the reusable burn-in fixture.
In another example, the variation in the height of contacts of a semiconductor substrate is compensated by a probe card used in a test assembly that may have a number of contact pins or needles extending from it on one side that contact the PCB and an opposite set that contact the semiconductor substrate under test. The individual pins or needles are typically co-planar. In compressing the testing assembly to make contact with the semiconductor substrate under test, the probe card may lose co-planarity to make contact with either the semiconductor substrate under test, resulting in poor alignment with the opposite set resulting in the problems during testing of current leak, poor connections, missing connections, etc.
One attempt to deal with these problems has been the use of “pogo” or spring loaded pins in a probe card. In the testing assembly, a keeper plate has a plurality of pogo pins, each pogo pin having a top side, a bottom side and a central sleeve containing the springs, inserted into holes in the keeper plate. One end of each pogo pin corresponds to a contact on the semiconductor substrate under test, while the opposite end corresponds to contact on the PCB. Such a keeper plate can adjust for some variation in the height of the contacts. However, each pogo pin has a cost of approximately $1.00, and must be assembled in the keeper plate. For a wafer-sized keeper plate, between 11,500 and 12,000 or more pogo pins may be needed. As such, the costs in materials and labor to manufacture such a keeper plate for a test assembly are significant.
Accordingly, a test apparatus or test system must have the pins in a probe card capable of compensating of any height variations of the contacts of a semiconductor substrate under test. Preferably, such a test apparatus or test system needs to be readily manufactured using standard micromachining or wafer handling techniques. Such a test apparatus or test system must be conveniently scalable from single semiconductor die testing to wafer-level testing.